The present invention relates generally to inducting devices incorporated in integrated circuits and in particular the present invention relates to an integrated circuit having an inducting device with a symmetric inductor.
Integrated circuits incorporate complex electrical components formed in semiconductor material into a single circuit. Generally, an integrated circuit comprises a substrate upon which a variety of circuit components are formed and connected to form a circuit. Integrated circuits are made of semiconductor material. Semiconductor material is material that provides for the formation of junctions depending on how it is doped, and by the fact that the resistance of the semiconductor material can vary by many orders-of-magnitude, also depending on the concentration of impurities or dopants. Semiconductor material is used to make electrical devices that exploit these properties.
It is desired to design integrated circuits in which electrical components and circuits within the integrated circuit do not interfere with each other. One method of accomplishing this is through the use of differential circuits. A differential circuit is a circuit that is really two circuits with opposite voltages and currents. That is, a differential circuit comprises a first circuit that produces desired voltages and currents and a second circuit that is identical to the first circuit that produces opposite voltages and currents. The opposite voltages and currents work to cancel out parasitics that naturally occur and helps to isolate the circuit from other circuits in the integrated circuit. Further discussion on parasitics can be found in commonly owned U.S. Pat. No. 5,717,243 and U.S. application Ser. No. 10/039,200 which are both incorporated herein by reference. An example of a useful device in a differential circuit is a symmetric inducting device. Symmetric inducting devices can be useful as part of a balun or transformer. Examples of symmetric inducting devices are illustrated in the U.S. application Ser. No. 10/039,200. It is desired in the art to have a symmetric inducting device that has less device area and has less resistive loss without introducing other parasitics.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an integrated circuit with a symmetric inducting device that has reduced resistive loss with low parasitic characteristics and reduced device area.
The above-mentioned problems and limitations of existing inductors in integrated circuits and other problems in inducting devices such as transformers or baluns that are composed of more than one inductor are addressed by embodiments of the present invention and will be understood by reading and studying the following specification.
In one embodiment, an inducting device comprises a first and second inductor. The first inductor is formed in a first conductive layer and is approximately symmetric about a plane of symmetry. The second inductor is formed in a second conductive layer that is at a select vertical distance from the first conductive layer. The second inductor is further approximately laterally aligned laterally with the first inductor.
In another embodiment, another inducting device for an integrated circuit is disclosed. The inducting device of this embodiment includes a first inductor and one or more secondary inductors. The first inductor is formed in a first conductive layer and is symmetric about a plane of symmetry. Each secondary inductor is formed in an associated secondary conductive layer a select vertical distance from the first conductive layer. Moreover, each secondary inductor is further generally laterally aligned with the first inductor and is positioned at a different vertical distance from the first inductor than any other of the one or more secondary inductors.
In another embodiment, still another inducting device for an integrated circuit is disclosed. The inducting device comprises a substrate, a first inductor, a second inductor and a layer of shield sections. The substrate has a working surface and a second surface opposite the working surface. The first inductor is formed from a conductive layer overlaying the working surface of the substrate. The first inductor has turns that are approximately symmetric about a plane of symmetry. A second inductor is formed in a conductive layer that is a select distance from the first inductor. Moreover, the first inductor is positioned between the second inductor and the working surface of the substrate. The layer of shield sections are positioned between the second surface of the substrate and the first inductor. The shield sections are more conductive than material they are directly adjacent.
In another embodiment, a method of forming an inductive device in a device region of an integrated circuit is disclosed. The method comprises patterning a first conductive layer into one or more inductor turns that are generally symmetric about a plane of symmetry to form a first inductor and patterning a second conductive layer into one or more inductor turns to form a second inductor that is laterally aligned with and a select vertical distance from the first inductor.
In yet another embodiment, another method of forming an inductive device in an integrated circuit is disclosed. The method comprises forming a first conductive layer overlaying a working surface of a substrate. Patterning the first conductive layer to form one or more inductor turns of a first inductor, wherein the one or more inductive turns of the first inductor are formed approximately symmetric about a plane of symmetry of a first inductor. Forming a dielectric layer overlaying the one or more inductor turns. Forming a second conductive layer overlaying the dielectric layer and patterning the second conductive layer to form one or more turns of a second inductor.